From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH] x86: Don't honour ACPI indicating absence of CMOS RTC Date: Tue, 17 Jun 2014 11:47:10 -0400 Message-ID: <20140617154710.GB7205@laptop.dumpdata.com> References: <1403017131-23790-1-git-send-email-andrew.cooper3@citrix.com> <53A07700020000780001B26F@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <53A07700020000780001B26F@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Andrew Cooper , Keir Fraser , Xen-devel List-Id: xen-devel@lists.xenproject.org On Tue, Jun 17, 2014 at 04:12:32PM +0100, Jan Beulich wrote: > >>> On 17.06.14 at 16:58, wrote: > > This reverts f74556693 "x86: honor ACPI indicating absence of CMOS RTC" > > > > Certain HP Gen8 BIOSes have started setting this bit despite an RTC CMOS > > being present and working. > > > > Their reasonsing is to prevent EFI-booted OSes from playing with the CMOS, > > combined with the erroneous assumption that the only OSes using legacy boot > > are too old to know about ACPI v5 and therefore to understand this bit. > > Which implies you can boot from EFI on those systems, which is > precisely what the panic message says you ought to do. Why do > you not boot via EFI in the first place? You can swap between legacy and EFI in the BIOS. Customers can choose either option. > > > As a result, the change being reverted prevented modern Xen from booting on > > modern HP hardware, despite older Xen working perfectly fine on the same > > hardware. > > Still, the flag has a purpose, and HP assigning a slightly non-standard > meaning to it doesn't mean we should outright revert that change. > Options I could live with (short of them revisiting the bogus assumption) > are > - a command line option suppressing the mandated behavior, > - a DMI quirk suppressing the mandated behavior, > - code probing for a functional CMOS RTC gating the panic() > invocation. That is probably the best option. The DMI is going to get large as it would probably include the G8 family. > > Jan > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel